Prevention of HIV infection in adolescent females is a continuing public health problem globally, especially in sub-Saharan Africa, where adolescent females are three times more likely to be HIV-infected than adolescent males. Recent studies have shown that adolescent females who are sexually vulnerable are at greater risk of HIV than those who are not sexually vulnerable. Based on published data from Rakai, sexual vulnerability is defined as early sexual debut, experiencing sexual coercion and engaging in cross- generational sex. Despite such advances, few studies have examined the factors that make adolescent females sexually vulnerable in sub-Saharan Africa. The proposed study theorizes that the family environment plays an integral role in adolescent females'sexual vulnerability as well as sexual risk behaviors. Studies have not longitudinally explored the influence of family environment on sexual vulnerability internationally nor have studies investigated the pathways through which family environment might affect HIV sexual risk behavior in female adolescents. Using 15 years of longitudinal data from the Rakai Health Sciences Program community cohort study (RCCS) in rural southwestern Uganda, the proposed study will use secondary data analysis to examine the influence of family environment on sexual risk behavior among females, ages 15 to 19. The specific aims of this study are to: 1) examine the effects of family environment on female adolescents'sexual vulnerability and 2) examine whether the pathway in which family environment affects female adolescent's HIV sexual risk is direct or is mediated by the adolescent sexual vulnerability status. The study populations are females who were a part of the RCCS during their adolescent years between 2002 and 2008. Using answers from the annual survey administered to the cohort, HIV-sexual risk behaviors will be measured as use of condoms and having multiple sexual partners and family environment will be operationalized in terms of eight dimensions, such as structure, size and presence of HIV in the home. Study aims will be addressed using generalized estimation equation analyses, survival analyses, structural equation models and epidemiological models. Findings will inform efforts to protect female adolescents from sexually vulnerable situations and to reduce HIV prevention efforts among adolescents, especially in developing settings. It will add to research on how families and households affect adolescent well-being and development. The results can enhance the effectiveness of HIV intervention designs that employ multiple levels of influence in similar settings as well as inform policies and create programs that incorporate the family into their initiatives.